Cables, in particular cables used in the offshore industry, can be extremely long and heavy. The cables must often be pulled from one location to another, requiring great pulling forces up to several tons. The cables must often be protected from the environment and physical impacts, and in certain applications cables are arranged concentrically inside a protective conduit that is pulled along with the cable and secured to a structure. An example of such an application is cables stretched between offshore wind turbines, transformer stations and the like. Another example of such an application is flexibles stretched between offshore production platforms.
In such an application, it is desirable that the conduit be secured to the entry point of the foundation, to ensure that the conduit is not pulled back out of the foundation by the weight of the cable arrangement, by currents or other forces. A prior art solution to this problem is disclosed in EP2329174. As shown therein, a lockable pull-in member is arranged at the end of the conduit. The pull-in member comprises a flexible bend restriction section at its leading end, and a locking segment at its trailing end. The flexible bend restriction section is made of a polymer material, while the locking segment is in the form a rigid, cylindrical steel body with an abutment portion at its base that has a larger diameter than the entry hole. The locking segment further comprises a plurality of biased, spring-loaded fingers spaced a distance forward of the abutment portion. The fingers, being biased in the extended position, spring out to engage the inside of the opening to prevent the conduit from being pulled back out of the structure.
Another example of a foundation pull-in interface is the invention by the present applicant in PCT/EP2017/063695, claiming priority from U.S. 62/347,367 filed Jun. 9, 2016, the entire contents of which is hereby incorporated by reference. As described therein, that application provides a foundation interface device comprising an elongated pull-in member for connection to a leading end of a flexible, elongated cylindrical conduit in which is arranged a cable. The pull-in member has a longitudinal central bore. At the trailing end of the pull-in member, a slidable sleeve is arranged about the circumference of the pull in member. The slidable sleeve is arranged to slide in the longitudinal direction of the pull-in member. The slidable sleeve has an abutment portion at its base, the abutment portion being larger in diameter than the opening of the foundation into which the pull-in device is to be pulled. The slidable sleeve is connected to extendable teeth members at its forward end by a linkage, whereby the longitudinal movement of the sleeve is transferred to a lateral extension of the teeth members, which engage the inside of the opening in the foundation to prevent the interface device from being pulled out.
The offshore foundations into which the above described interface devices are inserted are typically made of metal, for example carbon steel. The teeth or arms of the above described interface devices that engage the inside of the opening are likewise made of metal. Because of the saline environment of the seawater, the metal-to-metal contact between the teeth of the interface and the inside wall of the foundation will cause galvanic corrosion (also called bimetallic corrosion). Since such interface devices often have an expected lifetime of 20 years or more, such galvanic corrosion can weaken the wall area in the vicinity of the opening. Due to the sometimes extreme pulling forces from subsea cables, this can lead to catastrophic failure of the interface device.